ROLE OF MICRO-CHIMERISM IN INDUCING IMMUNOLOGICAL-TOLERANCE BY INTRAPORTAL INJECTION OF DONOR SPLEEN-CELLS IN RATS

Recently, we reported that intraportal (IF) injection of donor spleen cells (SPCs) prevented liver allograft rejection. Moreover, we develop ed a new method using polymerase chain reaction (PCR)-mediated restric tion fragment length polymorphism (RFLP) analysis, and demonstrated mi cro-chimerism (MC) at the DNA level in the spleen 14 days after IP inj ection. In the present study, the long-term presence of injected allog eneic SPCs was investigated at the cellular level by immunofluorescenc e staining as well as the DNA level using RFLP analysis. Male ACI (RT1 (a)) rats were used as the donors and Lewis (RT1(1)) rats as the recip ients. After DNA preparation from the lymphoid organs, RT1B beta domai n 1 region was amplified by PCR, and RFLP analysis was performed with PvulI restriction enzyme. In the immunofluorescence staining, the mono clonal antibody, MN4-91-6, was used to detect the injected donor ACI S PCs in a frozen specimen. We did not detect MC in Lewis rats intraveno usly injected with 5 x 10(7) ACI SPCs on day 14. On the other hand, st able chimerism in the spleen was observed in intraportally injected ra ts up to 28 days after injection at not only the DNA level but also th e cellular level. No chimerism was detected in other organs (including the thymus, lymph nodes, and liver). In conclusion, the long-term pre sence of injected allogeneic SPCs in the spleen was demonstrated after IP injection but not after IV injection, and this phenomenon may be o ne of the mechanisms involved in portal venous immunosuppression.